The present invention relates to a method and an apparatus for the production of a process gas for the treatment of substrates, especially semiconductor substrates.
Computer chips, as well as other electronic components, are manufactured on semiconductor disks, so-called wafers. For this purpose, many operating steps and processes are necessary, such as, for example, structuring, lithography, ion implantation, etching or coating. Coating processes are frequently carried out during a thermal treatment of the wafers in a prescribed process gas atmosphere. In this connection, it is known to use a process gas comprising water vapor and oxygen for an oxygen-rich wet oxidation of the wafers. The oxygen-rich process gas is particularly suitable for building up thick oxide layers of 2000 angstroms at low thermal budget, as well as for the production of thin gate-oxides having a layer thickness of less than approximately 40 angstroms. Furthermore, a hydrogen-rich wet oxidation is known according to which the process gas comprises water vapor and hydrogen. The hydrogen-rich process gas is particularly suitable for the selective oxidation of gate-stacks with metal gates or metal gate contacts.
For the production of the oxygen-rich process gas and of the hydrogen-rich process gas (i.e. a process gas comprising water vapor and oxygen or hydrogen), different methods were used in the past.
The oxygen-rich process gas was, for example, produced in a burner having a combustion chamber in which oxygen and hydrogen were burned to produce water vapor. For the combustion, more oxygen was always made available than could be burned with the hydrogen. In this way, there resulted an excess of oxygen, so that a process gas comprising water vapor and oxygen was formed. This process gas was subsequently conveyed via an appropriate conduit into a process chamber for the treatment of a semiconductor wafer. Additional oxygen could be introduced into the conduit in order to establish the oxygen content in the process gas.
For the production of a hydrogen-rich process gas, in the past hydrogen gas was mixed with water vapor, whereby the water vapor was produced by the evaporation of distilled water. However, this method does not permit high gas flows. Furthermore, the ratio of water vapor and hydrogen cannot be precisely controlled and reproduced. A further drawback of this method is that contaminations frequently occur.
Proceeding from the known state of the art, it is therefore an object of the present invention to provide a method and an apparatus which, in a straightforward and economical manner, enable the production of a hydrogen-rich process gas comprising water vapor and hydrogen, whereby the mixture ratio of water vapor and hydrogen can be precisely controlled and reproduced.